(Reuters) - Rare earth metals are making headlines as demand rises for products from smartphones to wind turbines, and as governments seek secure supply.

Here are some basic facts about them:

WHAT ARE THEY?Rare earths are a group of 17 elements including 15 silvery-white metals called lanthanides, or lanthanoids, plus scandium and yttrium. WHAT ARE THEY USED FOR?They are used in a wide range of products including consumer electronics, electric vehicles (EVs), aircraft engines, medical equipment, oil refining, and military applications such as missiles and radar systems.WHAT COUNTRY IS THE BIGGEST PRODUCER?China accounts for about 60% of global mine production and 90% of processed and permanent magnet output. Beijing sets quotas on output, smelting, and separation, which are closely monitored as a barometer of global supply. WHAT ARE THEIR NAMES? In their periodic table order, they are: scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.WHICH ONES ARE MOST COMMON?Lanthanum and cerium are among the most common rare earth metals. Lanthanum is used in camera lenses and lighting. Cerium is used in catalytic converters, which reduce combustion engine emissions.

Neodymium and praseodymium are in demand for permanent magnets used in EV motors and wind turbines.ARE THEY RARE?They are not rare in the sense that they are uncommon; some are more common than lead, for example. But they tend to be spread thin around the Earth's crust in small quantities and mixed together or with other minerals, so larger deposits are difficult to find and costly to extract.WHAT ENVIRONMENTAL IMPACT DO THEY HAVE?Processing rare earths often involves the use of solvents, which can produce toxic waste that pollutes the soil, water, and atmosphere. More environmentally friendly technologies are being developed, but they are not yet widely used.

Certain types of rare earth ores also contain radioactive thorium or uranium, which is often removed using acid.

For this reason, development of the sector faces health and environmental regulatory hurdles.